Unconjugated plasma estriol (E3) will be measured in 1,000 pregnant women attending our largest antepartum clinic at or around 31, 33, 35, 36, 37 and 38 weeks of gestation. These women with apparently uncomplicated pregnancies at the time of enrollment into this study will be randomly divided into a study and a control group. If plasma E3 levels or patterns are abnormal, study subjects will be referred for serial urinary E3 assays, oxytocin challenge tests (OCT's) and amniotic fluid lecithin/sphingomyelin (L/S) ratio analysis as well as appropriate clinical management. Plasma E3 results of control subjects will not influence clinical decisions. Fetal outcome of both groups will be compared to determine whether antepartum plasma E3 screening is of clinical value. Unconjugated plasma E3 will be measured twice weekly in gravidas who are at term but have uncertain dates or who, by history, are at or beyond 42 weeks of gestation. These patients will be managed clinically by twice weekly urinary E3 assays, weekly OCT's and, if necessary, L/S ratio determinations. Thus the study will demonstrate whether unconjugated plasma E3 may be used to distinguish between inaccurate dates, prolongation of gestation and true postmaturity. BIBLIOGRAPHIC REFERENCES: Katagiri, H., Distler, W., Freeman, R.K. and Goebelsmann, U.: Estriol in pregnancy. IV. Normal concentrations, diurnal and/or episodic variations, and day-to-day changes of unconjugated and total estriol in late pregnancy plasma. Am. J. Obstet. Gynec. 124:272, 1976. Freeman, R.K., Goebelsmann, U., Nochimson, D. and Cetrulo, C.: An evaluation of the significance of a positive oxytocin challenge test. Obstet. Gynec. 47:8, 1976.